1. Sulphur Mineral
The essential determination is that of the sulphur content. The sample
should be as representative as possible of the bulk and should be at least
5 kilos, this being finely powdered and well mixed.
Determination of the Moisture and of the Sulphur.—5-10 grams
are heated in a porcelain dish at 100° to constant weight; the loss represents
moisture. The dry sulphur is then placed in a filter-paper cartridge (finger)
and extracted with pure carbon disulphide (free from residue) in a Soxhlet
apparatus. The solution is evaporated carefully (carbon disulphide being
inflammable) and the residue dried at 70-80° and weighed. This gives the
sulphur content provided that the mineral contains no appreciable amount
of bituminous substances.
The latter are soluble in carbon disulphide and yield a brown or blackish
deposit on the walls and bottom of the vessel (see Crude sulphur, i). In
such case the sulphur in the extract is determined by one of the follow-
ing methods 1:
(a) FRESENIUS AND BECK'S METHOD. This method requires at least
10 grams of residue (sulphur and bitumen) from the carbon disulphide
8-10 grams of the residue are weighed into a porcelain crucible glazed
inside and outside, this crucible being then placed inside a second only
slightly larger, immersed to its rim in a sand-bath. The temperature of the
sand is then maintained at 200-220° for 7-8 hours and the crucible weighed
when cool. After a further hour's heating, the crucible is again weighed,
this being repeated until no loss of weight occurs.
The loss of weight at 200° represents the sulphur. The residue in the
crucible is then ignited until all carbonaceous matter disappears, the new
loss of weight giving the bitumen.
(b) MANZELLA AND LEVI'S METHOD. This method requires a conical
flask of about 100 c.c., with a ground-in air-condenser tube 40 cm. long and
6 mm. bore, the whole being of Jena glass.
0-2 gram of the residue from the carbon disulphide extraction is weighed
into the flask, the tube fitted into place and the flask immersed in cold
water. Through the inclined tube, 10 c.c. of fuming nitric acid (D = 1-52)
and 5 drops of bromine are introduced and the flask shaken until most of
the sulphur and bromine are dissolved, 5 c.c. of fuming nitric acid being
then added and the flask again shaken for some time. The flask is then
heated gently (the water not boiling) in a water-bath for about half an hour.
The flask is again immersed in the cold water and 50 c.c. of cold water added,
by the tube, drop by drop to avoid any violent evolution of red vapourt.
The solution is then transferred to a porcelain dish together with the wash-
ings of the flask and tube and evaporated to a small volume, a few drops of
cone, hydrochloric acid being added and the liquid again evaporated. The
residue is taken up in water'and made up to 400-500 c.c. in a beaker, the
solution being heated to boiling with i c.c. of cone, hydrochloric acid and
5% barium chloride solution in slight excess added drop by drop and with
1 M. G. Levi: "Methods of Analysis of Sulphur" (Ann. di chim. applic., 1915, i, p. 9).r are dissolved in nitric acid, 250 c.c. of ammonia being